Psychics are used to give detectives foreknowledge of someone's criminal intentions.

The FAST system is instead based on equipment including infrared cameras and pressure pads to detect fidgeting.

Details of the system were obtained through freedom of information laws by the Electronic Privacy Information Centre (Epic) based in Washington DC.

A document they obtained said that "sensors will non-intrusively collect video images, audio recordings, and psychophysiological measurements".

Ginger McCall, a lawyer for the non-profit group, told CBS News: "If it were deployed against the public, it would be very problematic.

"They should do a privacy impact assessment. Especially if they're going to be rolling this out at the airport."

Department of Homeland Security spokesman Peter Boogaard told the technology website CNET that "preliminary research" had been carried out to see if the technology could detect signs of stress, which can be associated with intent to do harm.

According to the documents obtained by Epic, the next trial may involve volunteer members of the public with experience in the food service industry.

They would be asked to work at a "one day VIP event" and some of them would be told to do something wrong, like smuggling in a recording device. The technology would then be used to identify the perpetrators.

A Homeland Security spokesman said the FAST experiments were voluntary and did not store any information from those involved.

He added: "If it were ever to be deployed, there would be no personally-identifiable information captured from people going through the system."